1. Field of the Invention
This invention relates to a lighting device used for illuminating a display device which does not emit light itself and a beam light source suitable for using in the lighting device, particularly relates to a beam light source which enables a light incident surface of a light guide plate to be smooth, where the light guide plate disperses and emits light entering from the beam light source in a form of surface light.
2. Description of Prior Art
A display device which does not emit light itself such as a liquid crystal display can display an image clearly by reflecting light on a front surface of the display device or transmitting light from a rear surface of the display device.
A lighting device used for the display device which does not emit light itself includes a beam light source for emitting light in a form of beam light and a light guide plate for dispersing and emitting light emitted from the beam light source in a form of surface light.
Some beam light sources use a bar-shaped light emitting tube such as a cold cathode fluorescent tube, but recently a beam light source including a point light source such as a white LED lamp and a beam-shaped light guide for dispersing and emitting light emitted from the point light source in a form of beam light is commonly used in order to reduce power consumption.
As shown in a front cross sectional view of FIG. 9 illustrating a basic structure and a side cross sectional view of FIG. 10 schematically showing such the conventional beam light source, the beam light source includes point light sources 201, 202 respectively facing to both end surfaces 204, 205 of a beam-shaped light guide 203, and enables light emitted from both of the point light sources 201, 202 to enter both of the end surfaces 204, 205 of the beam-shaped light guide 203 without leak.
The beam-shaped light guide 203 includes a reflecting surface 206 having many of V-shaped grooves 206a for reflecting light incident from the end surfaces 204, 205 in a direction orthogonal to an axis of the beam-shaped light guide 203, and a light emitting surface 207 for emitting light reflected on the reflecting surface 206 outside the beam-shaped light guide 203.
The point light sources 201, 202 and the beam-shaped light guide 203 are arranged in a reflecting member 208 having a channel section shape. The reflecting member 208 controls a direction of the light emitted from the beam-shaped light guide 203. The reflecting member 208 including a silver reflecting surface 208a on an inner surface of the reflecting member 208, covers three side surfaces of the beam-shaped light guide 203 except for the light emitting surface 207. To be concrete, the reflecting surface 206 of the beam-shaped light guide 203 is positioned on a bottom of the channel section shaped reflecting member 208 and the light emitting surface 207 is positioned on an opening of the reflecting member 208 so that light is emitted from the light emitting surface 207 to the opening of the channel section shaped reflecting member. The light, as indicated by viewing angle characteristics 209, is deviated and is emitted irregularly. The distribution of the light varies depending on a distance from the point light sources 201, 202.
As shown in FIG. 10, the opening of the reflecting member 208 is closed by an end edge of the surface light guide plate 210, and all of light emitted from the beam light source 200 enters an end surface 211 of the light guide plate 210 which closes the opening of the reflecting member 208. The end surface 211 is formed in a rough surface having fine dots by crape process so that light is regularly distributed into the light guide plate 210 as indicated by viewing angle characteristics 212.
When the end surface 211 of the light guide plate 210 is a rough surface, cost for processing in the rough surface is required. In addition, this structure raises problems such that the incident light is not distributed regularly because of a draft angle of a mold for the light guide plate 210, a rough surface can not be processed because of difficulty in releasing the mold from the end surface 211, and the end surface 211 of a rough surface is likely to be damaged and generates resin powder when the surface 211 contacts with other object.
This invention was made to provide a beam light source and a lighting device using the same, which enables a light guide plate for receiving light to have a smooth end surface so that the conventional problems are solved.
A beam light source comprises a point light source, a beam-shaped light guide including a light incident surface for receiving light emitted from the point light source, many of reflecting surfaces for reflecting light received on the light incident surface to a direction orthogonal to an axis direction of the beam-shaped light guide, a light emitting surface for emitting light reflected on the reflecting surface, and a side surface opposite to the light emitting surface. The beam light source further comprises a reflecting member having a channel section shape for controlling an emitting direction of light emitted from the beam-shaped light guide, and a scattering reflecting surface, which is formed on at least a channel bottom surface of the reflecting member, for irregularly reflecting light. The light emitting surface of the beam-shaped light guide is arranged so as to face to the channel bottom surface of the reflecting member. Light emitted from the light emitting surface of the beam-shaped light guide is irregularly reflected on the scattering reflecting surface on the channel bottom surface to make viewing angle characteristics uniform. The light is transmitted from the light emitting surface of the beam-shaped light guide through the side surface, and is dispersed and emitted in a form of beam light from the side surface. A lighting device comprises the beam light source and a surface light guide plate for receiving light from the beam light source on one end surface and dispersing and emitting the light from either or both of front and rear surfaces in a form of surface light.
With this structure, light emitted from the point light source, transmitting through the light incident surface of the beam-shaped light guide, and received on the reflecting surface of the beam-shaped light guide is focused within a critical angle, which is determined by a refraction rate of beam-shaped light guide material, and travels in the beam-shaped light guide. A part of the light reaches to the reflecting surface, and the light having a greater angle than the critical angle to the reflecting surface regularly reflects and travels to the light emitting surface. The light which has a smaller angle than the critical angle to the light emitting surface is emitted from the light emitting surface to outside of the beam-shaped light guide.
The light emitted from the light emitting surface in such the way has deviation in the viewing angle characteristics and is emitted irregularly. In addition, the distribution varies depending on a distance from the point light source.
When the emitted light reaches on the scattering reflecting surface as a channel bottom surface of the reflecting member, the light is reflected to the beam-shaped light guide as reflecting light having approximately uniform viewing angle characteristics. The reflected light having approximately uniform viewing angle characteristics is incident from the light emitting surface of the beam-shaped light guide into the beam-shaped light guide. A part of the light is reflected on the reflecting surface, and the other is transmitted through the beam-shaped light guide and is emitted from a side surface opposite to the light emitting surface to outside of the beam-shaped light guide.
The light incident from the side surface opposite to the light emitting surface with the approximately uniform viewing angle characteristics is incident to the light incident surface of the light guide plate. Thus it is not necessary to make the light incident surface rough in order to have light distribution in the light guide plate uniform, so that the light incident surface can be a smooth surface.
Accordingly, cost for processing the light incident surface of the light guide plate into a rough surface can be saved. In addition, light distribution of the light incident to the light guide plate can be uniform irrespective of a draft angle of a mold, and it becomes easy to release from the mold for the light guide plate. Furthermore, even when the light incident surface of the light guide plate contacts with other object, the surface is prevented from being damaged and swarf is prevented from being generated.